Baseflow is the water in a river that comes from groundwater. Baseflow measurements on a river and its tributaries help water resource managers understand how sensitive local streams and rivers are to extendined dry weather conditions or changes in the groundwater table that can result from land drainage work, or groundwater extraction.

The RVCA operates a number of permanent streamgauges , where a continuous record of flow (including baseflow — measured through the dry summer months and frozen winter months) is maintained. However, they are few in number — generally only one or two within each major tributary of the Rideau.
 

The RVCA operates a number of permanent streamgauges , where a continuous record of flow (including baseflow — measured through the dry summer months and frozen winter months) is maintained. However, they are few in number — generally only one or two within each major tributary of the Rideau.  

Baseflow can be highly variable along the length of a stream, since it is influenced by geological (surficial soils and bedrock conditions) and the groundwater table. Measurements of streamflow are therefore needed at numerous locations in the watershed. The baseflow monitoring effort consists of collecting manual estimates of streamflow at as many locations in the watershed as possible when there is little or no rainfall or snowmelt runoff in the stream, to augment the continuous streamflow measurements obtained at the recording gauge(s). Baseflow measurements will be taken in the same sites every year to build a long term database. When sufficient data is collected from the baseflow monitoring sites, the relationship between the baseflow recorded at the permanent gauges and other points in the watershed can be derived.

When sufficient data is collected from the baseflow monitoring sites, the relationship between the baseflow recorded at the permanent gauges and otehr points in the watershed can be derived.

The RVCA conducted its first baseflow survey in the late summer and early fall of 2003. The Jock River watershed was explored and surveyed and the Tay River and Kemptville Creek watersheds were inspected for suitable baseflow survey sites. Due to a very wet autumn it was not possible to get excellent baseflow readings at many sites. Next summer and fall the Tay River and Kemptville Creek Watersheds will be completed and the Jock River watershed will be revisited, time and weather depending. Baseflow measurements will be taken at the same sites every year.

Streamflow is a measure of volume over time and reported in cubic metres per second (cms). Velocity is a measure of distance over time and is reported in metres per
second (m/s). There are two main methods used in the RVCA baseflow survey for
measuring streamflow: the velocity-area method and the volume-time method. Both
methods are commonly used in Ontario.  

The velocity-area method entails dividing the cross section of the stream in a number of smaller sections and measuring the velocity of the water in each section using a current metre. The flow is calculated in each section by multiplying the velocity by the area of the section. The total flow across the river is calculated by summing the flows calculated at each section.   

To measure streamflow using the volume-time method one times how long it takes to collect a known volume of water. This method is ideal for small flows passing through culverts at a road crossing. If the culvert is raised slightly from the ground a bucket or container of a known volume is placed under the stream falling from the culvert. The flow is calculated by dividing the volume of water collected by the time it takes for the stream to fill the container.  

The data set provided here includes the final calculated flow at the baseflow measurement site and the measurement method used. The data set is divided by the sub-watersheds of the RVCA: Jock River, Tay River, Rideau Lakes, Lower Rideau River and Kemptville Creek. The baseflow measurement sites in each sub-watershed are indicated. Currently there are baseflow sites in only the Jock River and Tay River watersheds.